1. Field of the Invention
The present invention generally relates to a position sensing device for sensing the position of an object.
2. Description of the Related Art
In conventional methods, when, for example, moving an optical lens in the optical axis direction, the amount of movement of the optical lens is measured by a position sensing device, such as a linear scale, to detect the position of the optical lens. Such a position sensing device includes a scale section (or a sensor section) secured to an object, such as an optical lens, and a sensor section (or a scale section) secured to a portion, such as a lens barrel. By detecting the relative movement of the scale section and the sensor section, the position sensing device acquires positional data.
To acquire the positional data, the position sensing device cuts out parts of a plurality of periodically changing signals having different phases and carries out an interpolation arithmetic operation on the cutout signals (for example, Japanese Patent Laid-Open No. 2000-356504, in particular, paragraphs 0022 to 0025 and FIGS. 5 and 6). This position sensing method provides relatively decent precision position sensing, and therefore, this method is used for measuring the amount of lens movement in optical apparatuses.
In such a conventional position sensing method, a position (hereinafter referred to as a “reference position”) used for calculating a relative measured position, is required. More specifically, a moving unit having a built-in optical lens having a light-shielding unit, and a reset sensor (e.g., a photo interrupter) is mounted on a portion (e.g., a lens barrel). In such a structure, the light-shielding unit blocks the optical path of the photo interrupter in accordance with the movement of the moving unit so that the output of the sensor changes from high to low or from low to high. Accordingly, a position detected at the change in the output of the sensor is defined as the reference position.
Some conventional position sensing devices cause the moving unit to be brought into contact with a mechanical stopper to define the contact position as a reference position (for example, Japanese Patent Laid-Open No. 6-102936, in particular, paragraphs 0031 to 0033 and FIG. 1).
In order to determine the relative position of an object, the reference position needs to be more accurately detected.
In general, by monitoring the output of the reset sensor, position data corresponding to the point, at which the output of the reset sensor changes, is defined as data representing a measured reference position.
However, since the position data is generated using a different system than the reset sensor (e.g., based on a plurality of periodically changing multi-phase signals), the position data may be shifted from data representing the actual reference position. In this case, an error occurs in the relative position (e.g., the lens position determined minus reference position) determined based on the measured reference position.
Even when a position, where a moving unit is brought into contact with a mechanical stopper, is defined as a reference position, as described in Japanese Patent Laid-Open No. 6-102936, position data generated based on the output of the sensor unit may be shifted from data representing the reference position.